1. Field of the Invention
The invention relates to a temperature-raising device and a temperature-raising method for raising a temperature of a battery mounted in a vehicle.
2. Description of Related Art
In the related art, an electric vehicle that uses a rotary electric machine as a power source is widely known, examples of which include a hybrid car and an electric car. In the electric vehicle, a battery is mounted in order to supply electric power to the rotary electric machine. The in-car battery is a secondary battery that can be charged and discharged. The in-car battery can be charged with electric power generated by the rotary electric machine and electric power from an external electric power supply. The in-car battery has a low charging capacity at a low temperature, and then the length of time that is required for charging increases due to a reduction in allowable charging current. In addition, the in-car battery cannot be charged or discharged in a case where the temperature of the in-car battery decreases to the point of reaching a freezing temperature.
In some cases, the electric vehicle is put into a plug-in connection state, where the in-car battery and the external electric power supply are connected to each other, for charging after being stopped. When an environmental temperature is low in this case, the temperature of the battery decreases with time, and a problem arises in the form of charging using the external electric power supply not being appropriately performed. In this regard, an increase in the temperature of the in-car battery by the use of a heater has been proposed so that the temperature of the in-car battery becomes equal to or higher than a reference value in the plug-in connection state. In addition, calculation of a battery temperature-raising time allowing for the environmental temperature has been proposed. For example, Japanese Patent Application Publication No. 2012-191781 discloses prediction of a battery temperature transition from the battery temperature and the environmental temperature at the current point in time and prediction of the battery temperature-raising time and electric power consumption. According to this technique, charging of the battery or the like can be efficiently performed.